Why UV Is Stronger at the Beach, on Snow, and at Altitude
Ski trips and beach days hit you with UV from below as well as above—here's the physics of reflection and thin air that makes them so deceptively intense.
According to the World Health Organization, fresh snow reflects so much UV it can nearly double your exposure, sand reflects about 15% and sea foam about 25%, and UV increases roughly 10% for every 1,000 metres of altitude as the atmosphere thins.
The World Health Organization stresses that reflective environments and altitude are independent UV amplifiers—snow, sand and thin mountain air can each meaningfully raise your effective exposure—so the same person who never burns in town can be caught off guard on a slope or shoreline.
Questions we get a lot
Why do people get sunburned skiing in winter?
The World Health Organization notes that fresh snow reflects so much UV it can nearly double your exposure. On top of that, UV rises about 10% for every 1,000 metres of altitude as the atmosphere thins. Combined with cold air that hides the sensation of burning, this makes winter mountain UV deceptively strong.
How much UV does sand and water reflect?
According to the WHO, sand reflects about 15% of UV and sea foam about 25%. That reflected radiation adds to the direct sunlight hitting you, which is part of why beach days lead to burns even when there's a breeze. It also reaches areas like under the chin that sunscreen often misses.
Does UV really get stronger the higher you go?
Yes. The WHO states that UV increases roughly 10% for every 1,000 metres of altitude because there is less atmosphere to absorb it. A mountain summit can therefore expose you to substantially more UV than sea level. That's why high-altitude hikers and skiers need diligent, frequently reapplied protection.
r/Skiing: 'How am I this sunburned in winter? I didn't even feel warm on the mountain.'